Lafont



March 5 M. LAFONT 3,124,774

PRECISION.POTENTIOMETER Filed July 5, 1962 United States Patent3,124,774 PRECESION POTENTIOMETER Michel Lafont, Paris, France, assignorto Les Laboratoires de Physique Appliquee, Paris, France, a corporationFiled July 5, 1962, Ser. No. 207,610 Claims priority, application FranceJuly 5, 1961 3 Claims. (Cl. 338162) The present invention relatesgenerally to electric precision potentiometers and, more particularly,to coils of otentiometers of the toroidal type having their slidingcontact efiecting a continuous rotation, with no provision for a stopmember; more particularly, it relates to the electrical insulation ofthe ends of said coil at their junction point.

In this class of potentiometer-s, the insulation of the ends of the coilis commonly obtained by separating the two end portions of the toroidalsupport carrying the coil by means of an isolating wedge inserted in thejunction plane thereof. This method is however rather difficult toachieve in practice since the upper portion of the isolating wedge usedmust in this case be exactly on a level with the turns of the winding,so as to allow the slider to pass without being interfered with.

According to the invention, the two end portions of the toroidal-shapedsupport of the potentiometer are directly joined together and a few ofthe end turns of the coil are cutout over a portion of their length withwhich the slider does not come into contact, said turns being located onboth sides of the junction plane of said end p ortions and covering up alength of said support which is slightly larger than the width of thecontact area of the slider.

Preferably, said turns are cut out by causing a substantially radialcavity or notch to be formed in the toroidal support, accommodatingtherein an isolating wedge which serves to accurately position thetoroidal support on its carrier element.

The invention will be best understood from the following description andappended drawing, the single figure of which illustrates, by way of anunlimitative example, on a greatly enlarged scale, the two ends of atoroidal winding, in which a few of the end turns of the winding havebeen cut out.

Referring to the drawing, a toroidal support 1 is shown having thereon awinding 2, a sliding contact 3 and two terminal voltage taps 4 and 5.Said taps may be for instance keyed between an isolating wedge 6 and a.carrier portion 7 of the toroidal support.

The various components described being well known in the art, have beenillustrated in the drawing in a very diagrammatic manner only, sincethey may assume any desired shapes.

According to the invention, a substantially radially extending cavity orrecess 8 has been formed in the toroidal support 1. Said recess islocated about the junction plane 9 of the two end pieces 10 and 11 ofthe toroidal support and is arranged to sever three turns of the winding(although this number is in no way limitative) over a given portion oftheir length. Said turns normally adhere to the support and cannottherefore get loose from member 1; they simply play a mechanical partwhich consists in ensuring the passage of the sliding contact 3.

The width of the dead area thus formed may obviously 2 be readilyadjusted, which is a highly desirable feature of this invention. It musthowever remain greater than the contact area of the slider so as toavoid a short-circuit at the passage thereof, and smaller than thedistance separating the terminal supply contacts 4 and 5 of the potentiometer.

Said recess in the support may be for instance formed by milling thealready manufactured toroidal support members.

As noted the recess serves to accommodate the isolating wedge 6, thusensuring an accurate positioning of the toroidal member on carrierelement 7.

It is to be understood that various modifications may be brought to theembodiment described and illustrated, without departing from the spiritand scope of the invention.

What is claimed is:

1. *In a potentiometer of the continuous rotation type: an electricalresistance coil having a plurality of turns; a toroidal insulatingmember for supporting said coil; two terminals electrically connected tosaid coil at two respective points thereof; said coil having a firstportion having turns which are cut out over a part of their length and asecond portion having complete turns, said first portion being locatedin the space between said two points, the cut-out turns individuallyadhering on said insulating member, whereas the complete turns arespirally wound on said insulating member; a contact member in slidingrelationship with each of said cut-out and complete turns successively,whereby an electrical connection is established between said contactmember and said complete turns, while the cut-out turns co-operate withsaid contact member for ensuring the mechanical passage thereof.

2. In a potentiometer of the continuous rotation type: an electricalresistance coil having a plurality of turns; a toroidal insulatingmember for supporting said coil, said insulating member having two endportions joined together along a junction plane; two terminalselectrically connected to said coil at two respective points thereof,said coil having a first portion having turns which are cut out over apart of their length and a second portion having complete turns, saidfirst portion being located in the space between said two points, thecut-out turns individually adhering to said insulating member, whereasthe complete turns are spirally wound on said insulating member; acontact member in sliding relationship with each of said cut-out andcomplete turns successively, whereby an electrical connection isestablished between said contact member and said complete turns, whilethe cut-out turns cooperate with said contact member for ensuring themechanical passage thereof, said first portion substantially beingsymmetrically arranged with respect to said junction plane, saidtoroidal member having a radially extending recess located along saidfirst portion.

3. In a potentiometer of the continuous rotation type: an electricalresistance coil having a plurality of turns, a toroidal insulatingmember for supporting said coil, said insulating member having two endportions joined together along a junction plane; two terminalselectrically connected to said coil at two respective points thereof;said coil having a first portion having turns which are cut out over apart of their length and a second portion having complete turns, saidfirst portion being located in the space between said two points, thecut-out turns individually adhering to said insulating member, whereasthe 4 complete turns are spirally wound on said insulating mern-References Cited in the file of this patent her; a contact member insliding relationship with each UNITED STATES PATENTS of 58rd. cut-outand complete tur-ns successively, whereby n electrical connection isestablished between said con- 6 wzlmwnght 19:25 tact member and saidcomplete turns, While the out-out 5 4' Elliott Sept 8 turn cooperatewith said conta ot member for ensuring 2927293 D1011 1960 the mechanicalpassage thereof, said first portion sub- FOREIGN PATENTS stantiallybeing symmetrically arranged with respect t 1,103,756 France June 1 1955said junction plane, said toroidal member having a radial- 1y extendingrecess located along said first portion; an 10 isolating wedge beingaccommodated in said recess.

Notice of Adverse Decision in Interference In Interference No. 94,313involving Patent No. 3,124,774, M. Lafont, PRECI'SI ON POTENTI-OMETER,final judgment adverse to the patentee Was rendered Feb. 1, 1965, as toclaim 1.

[Ofiioz'al Gazette March 30, 1.965.]

Notice of Adverse Decision in Interference In Interference N0. 9%,313involving Patent No. 3,124,774, M. Lafont, PRECISION POTENTI-OMETER,final judgment adverse to the patentee was rendered Feb. 1, 1965, as toclaim 1.

[Ofiicial Gazette March 30, 1.965.]

1. IN A POTENTIOMETER OF THE CONTINUOUS ROTATION TYPE: AN ELECTRICALRESISTANCE COIL HAVING A PLURALITY OF TURNS; A TOROIDAL INSULATINGMEMBER FOR SUPPORTING SAID COIL; TWO TERMINALS ELECTRICALLY CONNECTED TOSAID COIL AT TWO RESPECTIVE POINTS THEREOF; SAID COIL HAVING A FIRSTPORTION HAVING TURNS WHICH ARE CUT OUT OVER A PART OF THEIR LENGTH AND ASECOND PORTION HAVING COMPLETE TURNS, SAID FIRST PORTION BEING LOCATEDIN THE SPACE BETWEEN SAID TWO POINTS, THE CUT-OUT TURNS INDIVIDUALLYADHERING ON SAID INSULATING MEMBER, WHEREAS THE COMPLETE TURNS ARESPIRALLY WOUND ON SAID INSULATING MEMBER; A CONTACT MEMBER IN SLIDINGRELATIONSHIP WITH EACH OF SAID CUT-OUT AND COMPLETE TURNS SUCCESSIVELY,WHEREBY AN ELECTRICAL CONNECTION IS ESTABLISHED BETWEEN SAID CONTACTMEMBER AND SAID COMPLETE TURNS, WHILE THE CUT-OUT TURNS TO CO-OPERATEWITH SAID CONTACT MEMBER FOR ENSURING THE MECHANICAL PASSAGE THEREOF.